This application is the National Stage of International Application PCT/FI00/00138 which was filed on Feb. 22, 2000 and designated the U.S. This International Application was published under PCT Article 21(2) in English.
1. Field of the Invention
The present invention relates to an apparatus for suppressing mutual interference between antennas located close to each other, said apparatus consisting of at least one elongated suppressing element of conductive material fitted between antenna radiators, disposed in a plane transverse to the connecting line between the antennas, wherein said suppressing element is disposed in the direction of radiation and has a length equal to a quarter or a multiple of a quarter of one of the wavelengths in the frequency range of the antennas, thus functioning as a resonator tuned at least to the frequency range in question, radiating in a plane transverse to the direction of radiation of the antennas. Such an apparatus is presented in U.S. Pat. No. 5,039,994.
2. Description of Related Art
The base transceiver stations of mobile communication networks use superposed dipole antennas, each antenna being connected to a separate transmitter-receiver apparatus. Such superposed antennas placed closely together produce interference in each other. For this reason, at present, superposed antennas must be placed at a relatively large distance from each other to achieve a sufficient insulation level, e.g. 26 dB, between the antennas. Therefore, the antenna structures currently used in base transceiver stations are relatively high. This is a disadvantage especially in cities, where there are many base transceiver stations within a small area and they are placed on residential and office buildings in city blocks.
Specification WO 98101923 presents a vertical cross-polarized antenna array which comprises a vertical suppression bar placed between superposed radiator modules, in a plane transverse to the direction of radiation, to suppress mutual interference between the antennas. The length of the bar is at least 25% of the distance between the radiator modules. In a dipole antenna structure presented in U.S. Pat. 3,541,559, the suppression bars are placed in a plane transverse to the direction of radiation and transversely to the connecting line between the antennas. The problem with these prior-art solutions for the suppression of interference is that they have a low interference suppression capability.
The object of the present invention is to eliminate the drawbacks associated with prior-art solutions and to achieve a new type of apparatus for suppressing mutual interference between antennas placed close to each other. The apparatus of the invention is characterized in that the antennas and the suppressing element are of electrically conductive film and etched on a fiberglass circuit plate.
Using the apparatus of the invention, it will be possible to place antennas considerably more closely together than at present. This will reduce the size of the antenna structures of e.g. base stations, allowing more inconspicuous disposition of the base stations of mobile communication networks especially in an urban environment.